Purpose: In stroke rehabilitation, exercises are used which require proprioceptive discrimination, whereby e.g. the hand is passively moved along two trajectories to identify spatial features. The neurological basis for this treatment is not fully understood. Therefore, we examined the cognitive process of shape and length discrimination, and looked at sensorimotor cortex reorganisation during passive movements in patients recovered from hemiplegia after stroke.
Relevance: To provide evidence for implementing discrimination tasks in therapy for hemiplegic patients, it is important to disclose the recruited brain network during discrimination exercises following passive movements. So far, no such study has been conducted in patients with stroke.
Participants: Eight patients (7 men, 1woman; mean age 61 years; range 41-74 years) were selected, based on having a subcortical infarct, good cognitive performance, right hemiparesis at stroke onset, and the ability to successfully differentiate imposed passive movements.
Methods: The finger of the patient was passively moved by a MRI compatible robot. Functional magnetic resonance imaging (fMRI) was used to detect brain areas related to discriminating different shapes (e.g. two rectangles) or the length of two lines based on passive finger movements. In this condition, music fragments were also presented but not attended to. This condition was contrasted to a matched control condition where music fragments had to be discriminated. In this condition, passive movements were also presented but not attended to. The rest condition bearded neither movement nor music.
Analysis: Using SPM99 software, we compared the results of the patients with stroke and healthy, age-matched controls using a 2-sample T test on: (1) shape and length discrimination versus music discrimination, (2) shape discrimination versus music discrimination, (3) length discrimination versus music discrimination; (4) shape and length discrimination versus rest, and (5) music discrimination versus rest.
Results: In both groups, shape discrimination resulted in activation of a lateral parietal-ventral premotor network, while length discrimination elicited a medial parietal-dorsal premotor network. Additional cerebellar activation was found in patients as compared to healthy volunteers. In shape and length movements versus rest, patients had expanded activation in premotor, sensorimotor and parietal regions. A striking difference was the bilateral sensorimotor activation in patients, compared to the contralateral sensorimotor activation in healthy volunteers, revealing an altered brain organisation in patients, despite their functional recovery.
Conclusions: Functional recovery in patients with stroke is often associated with altered patterns of brain activation. Nevertheless, the brain network responsible for cognitive processes related to shape and length discrimination was similar to healthy persons. We encourage research into the effect of therapy including discrimination exercises on brain reorganisation in patients with marked hemiplegia.
Implications: Our findings offer first insights into how cognitive processes are recruited during shape and length discrimination following passive movements in patients with stroke. This brain network shows an overlap with areas related to sensorimotor recovery. This may indirectly support the potential use of implementing these discrimination exercises in a therapeutic program. It would also be worthwhile investigating whether the bilateral sensorimotor network can be influenced by altering therapeutic strategies.
Funding acknowledgements: This work was supported by the Research Foundation-Flanders, Belgium.